1. Field of the Invention
The present invention relates to an electronic component and a manufacturing method for the electronic component, and more particularly to an electronic component having including external electrodes connected to an internal conductor and provided on the surface of a molded body having the internal conductor embedded therein and a manufacturing method for the electronic component.
2. Description of the Related Art
One electronic component, as shown in FIG. 10, is a surface mounting type inductor in which a pair of external electrodes 54a and 54b are electrically connected to end portions 52a and 52b of a conductor coil 52, on the surface of a molded body 53 arranged such that the coil conductor (internal conductor) 52 is embedded in a magnetic material 51 having a resin or rubber mixed with a magnetic powder and kneaded such that they are configured in a fixed shape. Conventionally, such an inductor is manufactured by a method described below.
Step 1
First, a molded body is formed, in which an air-core coil (internal conductor) defined by a wound copper wire is embedded in a resin or rubber mixed with a magnetic powder and kneaded such that both end portions of the air-core coil are exposed.
Step 2
Next, the surface of the molded body including the exposed portions of the air-core coil (internal conductor) is cleaned with alcohol or a neutral degreasing agent, and then etched to roughen the surface using an acidic or alkaline solution.
Step 3
Then, after the molded body has been immersed in a solution containing palladium ions, the palladium ions are reduced with a reducing agent to cause the metal palladium nuclei to precipitate onto the surface of the molded body.
Step 4
Next, electroless nickel plating is performed to form a metal film on the entire surface of the molded body.
Step 5
Then, after a necessary portion of the metal film has been coated with a resist, etching is performed to remove unnecessary portions of the metal film.
Step 6
Next, the resist is removed and various electroplating processes are performed on the metal film to form the external electrodes.
In this way, a surface mounting type inductor as shown in FIG. 10 is obtained.
However, when a metal film is formed by electroless plating, after the molded body is immersed in a solution containing palladium ions, the palladium ions on the molded body are reduced with a reducing agent, and then a palladium catalyst is provided on the surface of the molded body by precipitating the metal palladium nuclei, the adherence of a metal film provided on the surface of the molded body is affected by the adhesion of palladium nuclei, and thus, it is difficult to form a metal film having good adherence to both the surface of the molded body, which is made of a magnetic material having a resin or rubber as the main component, and is hereinafter, simply referred to as the molded body""s surface and the exposed surface of the internal conductor, which is hereinafter, simply referred to as the internal conductor""s exposed surface. Accordingly, to improve the adherence to both the molded body""s surface and the internal conductor""s exposed surface, strict control of the concentration and viscosity of a solution containing palladium ions and the conditions for electroless plating is required, which greatly increases to cost of producing the surface mounting type inductor.
To overcome the above-described problems, preferred embodiments of the present invention provide an electronic component including external electrodes having excellent adherence to both the molded body""s surface and the internal conductor""s exposed surface and having a greatly improved reliability and a manufacturing method for the electronic component.
The inventors have researched and investigated the relationship between the density of palladium deposited on the surface of the molded body and the adhesion of the electroless plating films. It was discovered that, in the method of electroless plating using palladium as a catalyst, 1) when palladium is densely deposited, the adhesion between a metal film formed by electroless plating and a molded body, preferably made of magnetic material including a resin or rubber as the main component, is good, but the adhesion between a metal film and the exposed portion of an internal conductor, preferably made of metal, is insufficient, and 2) on the contrary, when palladium is thinly deposited, the adhesion between a metal film formed by electroless plating and the exposed portion of an internal conductor, preferably made of metal, is good, but the adhesion between a metal film and a molded body, preferably made of magnetic material containing a resin or rubber as the main component, is insufficient. Furthermore, the inventors have conducted experiments on and investigated the relationship between the density of palladium deposited on the surface of a molded body preferably made of a magnetic material containing a resin or rubber as the main component, referred to as the molded body""s surface, and on the surface of the internal conductor exposed at the molded body, referred to as the internal conductor""s exposed surface, and the adhesion of an electroless plating film, which led the inventors to the present invention.
An electronic component according to preferred embodiments of the present invention includes an internal conductor made of a metal embedded in a molded body formed by molding an insulative material including a resin or rubber as the main component into a desired shape such that at least a portion of the internal conductor is exposed on the surface of the molded body, and external electrodes are connected to the internal conductor and are provided in a desired area, including the area where the internal conductor is exposed, on the surface of the molded body, and palladium is deposited at a deposition density of about 0.5 xcexcg/cm2 to about 1.5 xcexcg/cm2 on the surface of the molded body where the external electrodes are provided except at the area the internal conductor is exposed, palladium is deposited at a deposition density of about 0.05 xcexcg/cm2 to about 0.3 xcexcg/cm2 on the internal conductor exposed at the surface of the molded body, and a metal film, that defines at least a portion of the external electrode, is formed by electroless plating in the area where the palladium is deposited.
In the electronic component according to preferred embodiments of the present invention, palladium is deposited at a deposition density of about 0.5 xcexcg/cm2 to about 1.5 xcexcg/cm2 in the area where the internal conductor is not exposed within the area where the external electrodes are provided on the surface of the molded body, palladium is deposited at a density of about 0.05 xcexcg/cm2 to about 0.3 xcexcg/cm2 on the internal conductor exposed at the surface of the molded body, and a metal film, defining at least a portion of the external electrodes, is provided in the area where the palladium is deposited at a fixed density, which includes the molded body""s surface and internal conductor""s exposed surface. Accordingly, an electronic component having excellent adhesion between the metal film and both the molded body""s surface and the internal conductor""s exposed surface is provided, and a greatly improved external connection via the external electrodes is obtained.
That is, although the adhesion of a metal film to the molded body""s surface and the internal conductor""s exposed surface is affected by the density of deposited palladium (deposition per unit area), when the density of deposited palladium is within the above-described range, that is, a density of about 0.5 xcexcg/cm2 to about 1.5 xcexcg/cm2 on the molded body""s surface, and a density of about 0.05 xcexcg/cm2 to about 0.3 xcexcg/cm2 on the internal conductor""s exposed surface, it is possible to form a metal film which has excellent adhesion to both the molded body""s surface and the internal conductor""s exposed surface.
Furthermore, in an electronic component according to preferred embodiments of the present invention, both end portions of the internal conductor are exposed on the surface of the molded body and a pair of external electrodes is provided so as to be electrically connected to the both end portions.
Various preferred embodiments of the present invention are applicable to, for example, a surface mounting type inductor including a pair of external electrodes that are connected to both end portions of a conductor coil on the surface of a molded body formed such that the coil conductor (internal conductor) is embedded in a magnetic material having a resin or rubber mixed with magnetic powder and kneaded to produce a fixed shape. In this case, a metal film having excellent adhesion to both the molded body""s surface and the internal conductor""s exposed surface is provided. Thus, a highly reliable electronic component such as an inductor is provided.
Furthermore, in an electronic component according to a preferred embodiment of the present invention, the insulative material includes a resin or rubber that is mixed with a magnetic power and kneaded.
The present invention may also be applied to the case in which the insulative material includes a resin or rubber that is mixed with a magnetic powder and kneaded, and in this case a highly reliable electronic component, such as an inductor, having excellent adhesion between the external electrodes and the molded body, is provided.
Furthermore, in an electronic component according to a preferred embodiment of the present invention, the internal conductor includes a coil conductor defined by a spirally wound metal wire.
By applying various preferred embodiments of the present invention to, for example, a surface mounting type inductor, wherein external electrodes are provided on the surface of a molded body in which a coil conductor, that is, a spirally wound metal wire defining an internal conductor, a highly reliable electronic component having excellent adhesion between a metal film defining external electrodes and a molded body is produced.
Furthermore, in an electronic component according to a preferred embodiment of the present invention, the internal conductor is preferably made of at least one material selected from a group of Cu, Ag, Al, Ni, and their alloys.
Additionally, a manufacturing method of an electronic component according to the present invention includes the steps of embedding an internal conductor made of a metal in a molded body formed by molding an insulative material having a resin or rubber as the main component into a desired shape such that at least a portion of the internal conductor is exposed on the surface the molded body, depositing palladium on the surface of the molded body at a deposition density of about 0.5 xcexcg/cm2 to about 1.5 xcexcg/cm2 where the internal conductor is not exposed, and on the internal conductor exposed on the surface of the molded body at a deposition density of about 0.05 xcexcg/cm2 to about 0.3 xcexcg/cm2, forming a metal film on the surface of the molded body via electroless plating after deposition, and providing external electrodes, which are electrically connected to the internal conductor, in a desired area, including the area where the internal conductor is exposed, on the surface of the molded body.
After palladium has been deposited at a density of about 0.5 xcexcg/cm2 to about 1.5 xcexcg/cm2 in the area (molded body""s surface), in which the internal conductor is not exposed, on the molded body and palladium has been deposited at a density of about 0.05 xcexcg/cm2 to about 0.3 xcexcg/cm2 on the surface (internal conductor""s exposed surface) of the internal conductor exposed at the molded body, a metal film having excellent adhesion to both the molded body""s surface and the internal conductor""s exposed surface by conducting electroless plating is produced. Accordingly, a highly reliable electronic component is efficiently manufactured.
Moreover, where a metal film is formed on the surface of the molded body, when the deposition of palladium on the molded body""s surface is less than about 0.5 xcexcg/cm2, the adhesion between the molded body""s surface and the metal film greatly decreases, and furthermore, when the deposition of palladium on the molded body""s surface exceeds about 1.5 xcexcg/cm2, the segregation of palladium nuclei in the electroless plating solution greatly increases, thus causing the electroless plating solution to deteriorate and the cost to greatly increase. Accordingly, the deposition of palladium on the molded body""s surface is preferably within the range of about 0.5 xcexcg/cm2 to about 1.5 xcexcg/cm2.
Furthermore, when the deposition of palladium on the internal conductor""s exposed surface exceeds about 0.3 xcexcg/cm2, where a metal film is provided on the internal conductor""s exposed surface by a method of electroless plating, the adhesion between the internal conductor""s exposed surface and the metal film deteriorates, and moreover, when the deposition of palladium on the internal conductor""s exposed surface is less than about 0.05 xcexcg/cm2, the electroless plating is only partially conductive. Accordingly, it is preferable to set the deposition of palladium on the internal conductor""s exposed surface in the range of about 0.05 xcexcg/cm2 to about 0.3 xcexcg/cm2.
Furthermore, a manufacturing method for an electronic component according to a preferred embodiment of the present invention further includes the steps of roughening a predetermined area on the surface of the molded body, including the exposed portion of the internal conductor, by dry blasting, smoothing the exposed surface of the internal conductor, which is roughened by dry blasting, by immersing the molded body in an etching solution, and forming a metal film on the surface of the molded body including the exposed portion of the internal conductor by performing electroless plating after the smoothing process.
A metal film having excellent adhesion to both the molded body""s surface and the internal conductor""s exposed surface is provided by performing electroless plating after a fixed area on the surface of the molded body, including the exposed portion of the internal conductor, has been roughened by dry blasting, and then the exposed surface of the internal conductor is smoothed by immersing the molded body in an etching solution.
That is, the rate at which a palladium ion is reduced to metal palladium is low on the exposed surface of the internal conductor made of a metal, such as copper, having a greater ionization tendency than that of the palladium, and since the molded body""s surface is much rougher than the smoothed internal conductor""s exposed surface, palladium ions are more densely deposited on the molded body""s surface than on the internal conductor""s exposed surface because of the anchor effect. Therefore, by reducing the palladium ions deposited on the molded body""s surface using a reducing agent, the deposition of palladium on the molded body""s surface is much denser than the deposition of palladium on the internal conductor""s exposed surface. In the electroless plating process subsequently performed, an electroless plating film having excellent adhesion to both the molded body""s surface and the internal conductor""s exposed surface is efficiently produced.
Furthermore, a manufacturing method for an electronic component according to a preferred embodiment of the present invention further includes the steps of roughening only the surface of the molded body by immersing the molded body in an organic solvent, and thereafter forming a metal film in a desired area on the surface of the molded body, including the exposed portion of the internal conductor, by performing electroless plating.
By conducting electroless plating after only the surface of the molded body has been roughened by immersing the molded body in an organic solvent, the deposition of palladium on the molded body""s surface is denser than the deposition of palladium on the internal conductor""s exposed surface. Accordingly, a metal film having excellent adhesion to both the molded body""s surface and the internal conductor""s exposed surface in a fixed area on the surface of the molded body including the exposed portion of the internal conductor is efficiently produced.